In the manufacture of a communications cable, a core comprising a plurality of insulated conductors is enclosed in a strip of non-metallic material, which is referred to as a core wrap. Subsequently, the core wrap is enclosed by other components of a sheath system such as, for example, an aluminum shield and a jacket. The core wrap insulates the core from the aluminum shield which is designed to protect the cable core from lightning damage and from electrical disturbances. The core wrap and the shield, which often times is corrugated, are formed from continuous strips which are wrapped longitudinally with overlapped seams about an advancing cable core.
For some cables, a closed, unjoined overlapped seam for the shield is provided. In those, an outer overlapping edge portion of the metallic shield tends to rebound subsequent to forming and to project into an outer plastic jacket that is extruded around the shield. This problem has been overcome by methods and apparatus which are shown in U.S. Pat. No. 4,308,662 issued to W. D. Bohannon, Jr. on Jan. 5, 1982.
Typically, the strip of non-metallic material is wrapped about the core prior to the forming of the metallic shield thereabout. The non-metallic material, which may be a MYLAR.RTM. plastic material, is formed into an oversized core wrap by passing the strip through a tapered tube having overlapped but spaced apart edges which forms an overlapped seam. Afterwards, a binder ribbon is wrapped spirally about the strip to hold the plastic material about the core during movement along a manufacturing line to a metal forming station. The oversized plastic core wrap is drawn down tightly on the advancing core by the binder ribbon which is under tension. Subsequently, a second binder is wrapped spirally about the core wrap and the tension therein causes it to further draw down the core wrap. This may cause the first binder ribbon to become loose and possibly entangled with portions of the manufacturing apparatus. Also, if the second binder ribbon should break, the core wrap may be disposed somewhat loosely about the core by the time it reaches the metallic forming station.
This process for providing a core wrap has several other shortcomings. For example, the application of a binder to draw down the core wrap prior to the wrapping of a metallic strip thereabout requires the use of a relatively low line speed. Also, this process is wasteful from a material standpoint. When it is drawn down by the use of binder tension, the core wrap material tends to become wrinkled. To insure complete coverage of the core, the width of the strip of core wrap material is greater than the circumference plus overlap of a perfectly formed, non-wrinkled tubular cover. Further, because the strip of plastic material is wrapped about the core some distance prior to the forming of the metallic strip, it is required to have particular strength properties. As a result, the choice of materials for use as the core wrap has been somewhat limited.
Seemingly, the prior art is devoid of a solution of this problem. The prior art includes U.S. Pat. No. 3,615,977 which slows the formation of paper and metallic tubes having gapped longitudinal seams about an advancing core having annular discs spaced therealong. Filling material is introduced through the gapped seams after which opposing edges of the metallic tube are welded together. An arrangement for forming gapped seams is relatively simple, but does not provide a solution to the problems which are encountered as a non-metallic core wrap material and a metallic material are formed about an advancing cable core.